The purpose of the proposed research is to develop a set of tasks and procedures that will serve a larger research program addressing the early development of cooperative peer interaction in relation to developing social understanding. Cooperative play with peers is a primary context in which children acquire social, communicative, and interactive skills and in which they come to understand and use the intentions, desires, and mental states of others to predict and regulate their own and others' behavior. Although great strides are being made in describing social understanding in infants and toddlers, there is virtually no work addressing how this developing understanding is put to work in social interaction with other children. The long-term objective of the applicant's research program is to understand the origins and early development of cooperative peer interaction and its relation to developments in social understanding of both self and others. The aim of the particular research described in this proposal is to establish the tasks and procedures that will permit the programmatic study of these early developments. The proposed research has two specific aims: 1) to develop and test a new set of peer cooperation procedures for one and two year olds that are motivating, cognitively and motorically simple and readily achieved, as well as progressive in the nature of the social understanding required to achieve them; 2) to extend and modify procedures derived from tasks used by others to assess parallel developments in young children's self- and other-awareness, and to test hypotheses about their coherence and construct validity as well as their associations with age. The proposed research will build on methods used in the applicant's own past research, as well as those appearing more recently in others' research. A series of five successive cross-sectional studies is proposed to test and evaluate the tasks. Each study will include 18 and 24 month olds. [unreadable] [unreadable]